Vent valve

ABSTRACT

The invention concerns an air transfer valve which automatically vents accumulated air from pressurized liquid reticulation pipelines or vessels. The valve ( 10 ) has a housing ( 12 ) which is connectable to the pipeline or vessel. The housing has a first outlet ( 38 ) venting to atmosphere and a control chamber ( 60 ) which is exposed to internal pressure in the housing via a control chamber inlet. A first valve closure ( 34 ) can move to open and close the first outlet. This valve closure is exposed to control chamber pressure tending to move it to close the first outlet and to internal housing pressure tending to move it to open the first outlet. When the housing is pressurized the first valve closure ( 34 ) is maintained in a closed position by virtue of an unbalanced pressure force acting on it that is attributable to exposure of the valve closure to atmosphere through the first outlet. There is also a control chamber outlet ( 36 ) from the control chamber ( 60 ) to atmosphere. This outlet is larger than the control chamber inlet. The valve also incorporates a float ( 20 ) in the housing ( 12 ) which is arranged to be buoyed up by liquid entering the housing from the pipeline and a second valve closure ( 24 ) carried by the float which is arranged to open and close the control chamber outlet ( 36 ) in response to movement of the float caused by variations in the level of liquid in the housing. Downward movement of the float ( 20 ) in response to a drop in liquid level in the housing ( 12 ), attributable to accumulation of air in the housing, causes the second valve closure ( 24 ) to open the control chamber outlet ( 36 ). This allows the control chamber ( 60 ) to vent to atmosphere. The pressure in the control chamber ( 60 ) drops relative to the internal housing pressure and creates an unbalanced pressure force on the valve closure ( 34 ) which causes it to open the outlet ( 38 ). The housing can then vent to atmosphere via the outlet ( 38 ).

BACKGROUND TO THE INVENTION

THIS invention relates to an air transfer valve. The invention isparticularly concerned with an air transfer valve, otherwise known as anair release valve, which can be used to vent air from a pipeline inwhich a liquid is conveyed under pressure, or from other pressurisedvessels.

A known air transfer or release valve has a housing with an inlet at itslower end which is connected, typically at a high point, to a pipelinefrom which air is to be vented. The housing has an outlet at its upperend and in its simplest form accommodates a float. During pipelinefilling, the theory is that water or other liquid in the pipeline willenter the housing and buoy up the float to seal against the outlet. Airwhich then accumulates in the housing during operation of the pipelinewill cause the float to lose buoyancy with the result that it drops awayfrom the outlet to allow accumulated air to vent through the outlet toatmosphere.

In practice however, it has been observed that in many cases, the floatmay be “blown” closed during rapid pipeline filling and then be held ina closed position by the pressure in the pipeline. This may for instanceoccur in a situation where the valve is installed at a high point in thepipeline which is lower than another high point further downstream.During initial filling of the pipeline, air accumulating at the highpoint served by the valve will vent through the valve according totheory, but if such venting is not fast enough, an air pocket may beformed beneath the valve. The air in this pocket will be pressurisedrapidly by the pumping pressure and the downstream head of liquid.

The pressure differential acting across the valve float may in someinstances be sufficient to “blow” the float to a closed positiondynamically. The internal pipeline pressure may then maintain the floatin this closed position, preventing further venting through the valve.

Similarly, if the float has been hydraulically closed, i.e. it has beenbuoyed up by liquid in the housing to seal against the outlet, it mayremain in this condition by internal pressure in the pipeline. Stillfurther it is possible, during rapid pipeline filling, for liquid to belifted up by a bubble of air which enters the housing from the pipeline,and this can also cause the float to seal against the outlet. In any ofthese situations, the float may then be held closed by the elevatedinternal pressure forces until the pipeline is fully depressurised.

To address the problem of venting in internally pressurised situationsit has been proposed to provide a small bleed orifice through the floatto allow equalisation of the internal pressure. However a bleed orificecan only vent air very slowly and so is unable to achieve pressureequalisation fast enough for the float to drop down to allow therequired rapid venting of air to take place.

A known air transfer or release valve is described in the specificationof South African patent 87/5645 (ARI Flow Control Accessories). Thisvalve has a narrow outlet slot which is covered by a flexible stripattached to a float. Downward movement of the float in response to airaccumulation unpeels the strip incrementally from the slot and allowssmall volumes of trapped air to vent from the valve housing. A problemwith this design is that only small volumes can be vented through thenarrow slot.

Other solutions which have been proposed make use of mechanicallinkages. One example is described in the specification of U.S. Pat. No.5,090,439 (APCO). The air release valve described in this specificationoperates such that when the valve is closed, pressure-relatedforces-acting on the closure are balanced.

Only a buoyancy force acting on a float is operative to hold the valveclosure in a closed position. This facilitates valve opening even underpressurised conditions. However the design is such that when the floatloses buoyancy and the valve closure does open, the pressure in thefloat housing, which may be quite considerable, generates an unbalancedforce on the closure tending to hold it open.

It is an objective of the present invention to provide an alternativeair release valve which addresses the problem of air venting in apressurised system.

SUMMARY OF THE INVENTION

According to the invention, there is provided an air transfer valvecomprising:

-   -   a housing connectable to a pipeline or vessel which conveys or        contains liquid under pressure    -   a first outlet from the housing to atmosphere,    -   a control chamber exposed to internal pressure in the housing        via a control chamber inlet,    -   a first valve closure which is movable to open and close the        first outlet and which is exposed to control chamber pressure        tending to move it to close the first outlet and to internal        housing pressure tending to move it to open the first outlet,        whereby when the housing is pressurised the first valve closure        is maintained in a position closing the first outlet by virtue        of an unbalanced pressure force acting on it that is        attributable to exposure of the first valve closure to        atmosphere through the first outlet,    -   a control chamber outlet from the control chamber to atmosphere        which is larger than the control chamber inlet,    -   a float in the housing arranged to be buoyed up by liquid        entering the housing from the pipeline or vessel,    -   a second valve closure carried by the float which is arranged to        open and close the control chamber outlet in response to        movement of the float caused by variations in the level of        liquid in the housing,        the arrangement being such that downward movement of the float        in response to a drop in liquid level in the housing causes the        second valve closure to open the control chamber outlet,        allowing the control chamber to vent to atmosphere with the        result that pressure in the control chamber drops relative to        the internal housing pressure and creates an unbalanced pressure        force on the first valve closure which causes it to open the        first outlet, thereby allowing the housing to vent to atmosphere        via the first outlet.

Other features of the invention are defined in the appended claims.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be described in more detail, by way of exampleonly, with reference to the accompanying drawing which shows across-sectional view of an air transfer valve according to theinvention.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

The air transfer valve 10 illustrated in the drawing has a housing 12composed of upper and lower housing parts 12.1 and 12.2 screwedtogether. The lower housing part 12.2 defines an axial housing inlet 14at its lower end and the upper housing part 12.1 defines a primary,axial outlet 16 at its upper end which vents to atmosphere.

In use, the housing inlet 14 is connected to a pipeline which conveys aliquid, for convenience referred to herein as water, under pressure,typically at a high point in the pipeline.

The housing 12 accommodates a float 20 which is guided for up and downmovement in the housing 12 by means of spaced ribs 22.

A nipple 24 is engaged in an axial hole 26 in the upper surface of thefloat and extends above the float as illustrated. At its upper end thenipple carries a seal 28. The upper end of the nipple passes slidablythrough a disc-shaped control element 30 and enters a recess 32 in anupper, cap-shaped, valve closure member 34, referred to herein as thefirst valve closure. The first valve closure 34 carries a nozzle 36aligned axially with the seal 28 and passing through an outlet opening38, referred to herein as a first outlet, in a valve seat member 40. Thelower end of the first outlet 38 is bounded by a valve seat 42. Theupper surface of the member 34 carries a valve seal 44 aligned with thevalve seat 42.

The first valve closure 34 is fixed centrally to a resilient diaphragm46 the periphery of which is sandwiched and anchored between portions ofthe control element 30 and the valve seat member 40 which are clippedtogether at a circumferential clip formation 48. A flange 50 at thelower end of the valve closure 34 can slide up and down in a recess 52defined by the element 30.

In combination the element 30 and member 40 form a primary valve closure54 for closing the primary outlet 16.

The operation of the air transfer valve 10 at various stages isdescribed below.

Pipeline Filling

The float 20 and primary valve closure 54 are initially at a low levelin the housing 12.

As the pipeline fills and water enters the housing, displaced air canvent rapidly to atmosphere through the primary housing outlet 16. Therising water buoys up the float 20, causing the seal 28 to seat on thelower end of the nozzle 36. Thereafter the rising float 20 also liftsthe primary valve closure with the result that an O-ring 56 carried bythe member 40 of the closure 54 seats against an annular surface 58 ofthe housing part 12.1, thereby closing the primary opening 16.

Pipeline pressure can now build up to full working value in the housing.The internal housing pressure force acting upwardly on relevant surfacesof the primary valve closure 54 is greater than the sum of downwardforces acting on the closure as a result of atmospheric pressure,gravity and internal pressure forces. The differential upward pressureforce maintains the primary closure 54 in a closed position as long asthe pipeline and housing are pressurised.

The diaphragm 46 separates the hollow interior of the primary valveclosure 54 into a control chamber 60 beneath the diaphragm and apressure space 62 above the diaphragm. Internal housing pressure hasaccess to the control chamber 60 through a control chamber inlet formedby an annular clearance or gap which exists between the nipple 24 andthe opening in the element 30 through which the nipple passes. Thepressure space 62 is directly exposed to internal housing pressurethrough spaced apart ports 64 in the member 40.

Housing pressure which exists in the space 62 tends to bias thediaphragm downwardly while pressure which exists in the control chamber60 tends to bias the diaphragm upwardly. The inherent resilience of thediaphragm urges the first valve closure 34 against the seat 42 asillustrated in the drawing. Because a portion of the closure 34 isexposed directly to atmosphere via the first outlet 38, there is then anunbalanced, upwardly acting pressure force on the valve closure 34 whichmaintains it in this closed position.

Normal Operation

Air enters the housing 12 and accumulates therein under the prevailingpressure. When sufficient air has accumulated, the float 20 losesbuoyancy and drops. This unseats the seal 28 from the lower end of thenozzle 36. Pressurised air in the control chamber 60 can now vent toatmosphere through the nozzle. The cross-sectional area of the controlchamber inlet, i.e. the annular clearance or gap between the nipple andthe opening in the element 30 through which it passes, is less than thecross-sectional area of the nozzle passage. Air can accordingly ventmore rapidly through the nozzle than it can enter the control chamber 60from the housing. As a result the pressure in the control chamber 60drops relative to the pressure in the space 62. This gives rise to a netdownward pressure force on the diaphragm 46 which deflects the diaphragmdownwardly. This unseats the seal 44 of the first valve closure 34 fromthe valve seat 42 and allows air to vent rapidly from the housing viathe relatively large first outlet 38 and the primary outlet 16.

The nozzle 36 may be seen as a second outlet which is controlled by asecond valve closure, i.e. the nipple 24 and seal 28 carried by thefloat 20.

As air vents from the housing 12 the water level therein will rise tobuoy the float 20 up again, and the process repeats itself.

It will be understood that the nipple 24 does not drop completely belowthe element 30 when the float drops. This ensures that a limited controlchamber inlet, i.e. the annular gap between the nipple and the openingin the element 30 through which the nipple passes is always present tocontrol the rate at which air can enter the control chamber 60.

Pipeline Draining

When the pipeline drains at the end of a pumping cycle or otherwise,pipeline pressure drops. The float 20 and primary valve closure 54 dropdownwardly to their initial low positions, thereby opening the primaryoutlet 16 completely. At the commencement of the next pumping cycle, thesequence described above for “Pipeline Filling” will again take place.

It will be understood that the air transfer valve described above iscapable of opening a fairly large vent opening, namely the first outlet38, even when the housing 12 is internally pressurised. The describedair transfer valve therefore successfully addresses the problem of airventing under pressure.

It will also be understood that the air transfer valve has beendescribed above in an application in which it is used to ventaccumulated air from a pressurised pipeline, it could equally well beused to vent air from other pressurised, liquid-containing vessels.

1. An air transfer valve comprising: a housing connectable to a pipelineor vessel which conveys or contains liquid under pressure a first outletfrom the housing to atmosphere, a control chamber exposed to internalpressure in the housing via a control chamber inlet, a first valveclosure which is movable to open and close the first outlet and which isexposed to control chamber pressure tending to move it to close thefirst outlet and to internal housing pressure tending to move it to openthe first outlet, whereby when the housing is pressurised the firstvalve closure is maintained in a position closing the first outletsolely by virtue of an unbalanced pressure force acting on it that isattributable to exposure of the first valve closure to atmospherethrough the first outlet, a control chamber outlet from the controlchamber to atmosphere which is larger than the control chamber inlet, afloat movable vertically in the housing and arranged to be buoyed up byliquid entering the housing from the pipeline or vessel, a second valveclosure attached rigidly to the float such that vertical movement of thefloat directly causes the same vertical movement of the second valveclosure, the second valve closure being arranged to open and close thecontrol chamber outlet in response to movement of the float caused byvariations in the level of liquid in the housing, the arrangement beingsuch that vertical downward movement of the float in response to a dropin liquid level in the housing causes the same vertical downwardmovement of the second valve closure whereby the second valve closureopens the control chamber outlet to allow the control chamber to vent toatmosphere with the result that pressure in the control chamber dropsrelative to the internal housing pressure and creates an unbalancedpressure force on the first valve closure which causes it to open thefirst outlet, thereby allowing the housing to vent to atmosphere via thefirst outlet.
 2. An air transfer valve according to claim 1 wherein thefirst valve closure is carried by a resilient diaphragm one side ofwhich is exposed to pressure in the control chamber and the other sideof which is exposed to internal housing pressure.
 3. An air transfervalve according to claim 2 wherein the control chamber outlet extendsthrough the first valve closure.
 4. An air transfer valve according toclaim 3 wherein the control chamber outlet comprises a nozzle extendingthrough the first valve closure and the second valve closure is carriedby a nipple on the float which passes through an opening in the controlchamber with a clearance which forms the control chamber inlet, thecross-sectional area of the nozzle being greater than that of theclearance.
 5. An air transfer valve according to claim 4 wherein thefirst outlet, first valve closure and control chamber form a primaryclosure which is arranged to be raised by the float, to seat on andclose a primary outlet from the housing, when the float is buoyed up byliquid in the housing.
 6. An air transfer valve according to claim 5wherein the diaphragm spans across a hollow interior of the primaryclosure and subdivides that interior into the control chamber beneaththe diaphragm and a space above the diaphragm which is exposed tointernal housing pressure via ports in the primary closure.